Multi-stacked electronic device with defect-free solder connection

ABSTRACT

A method includes forming a multi-stacked electronic device having two or more electronic components, each of the electronic components includes a leadframe, the leadframes of each electronic component are physically joined together using a non-solder metal joining process to form a joint, and the joint is located outside a solder connection region.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of copending U.S. patent applicationSer. No. 14/332,776, filed Jul. 16, 2014, the entire contents anddisclosure of which are hereby incorporated herein by reference.

BACKGROUND

The present invention generally relates to electronic devices and moreparticularly to multi-stacked electronic devices having improvedsolderability.

A multi-stacked electronic device may be formed by two or moreelectronic components disposed one on top of another. Each electroniccomponent may include leadframes extending from the package. Theleadframes are external electrical connections that may allow to jointhe multi-stacked electronic device to printed circuit boards (PCBs) orother electronic devices. A soldering process may be typically conductedto attach the multi-stacked electronic device via the leadframes to thePCB. Prior to soldering the multi-stacked electronic device to the PCB,a metal joining process may be conducted to physically and electricallyconnect the leadframes of each electronic component.

The soldering process may generally include melting and flowing a filleror solder metal into a solder joint. Good solderability may be relatedto wetting by the solder material. When good wetting conditions areachieved, a uniform and adherent coat of solder may fill the solderjoint efficiently bonding the multi-stacked electronic device to thePCB. In contrast, if wetting conditions are not satisfactory, poorsolderability may be observed causing problems such as dewetting of thesolder joint. Dewetting may occur when the solder metal coating asurface withdraws from the solder joint creating irregularly shapedheaps of solder metal separated by areas covered with a thin film ofsolder metal. Dewetted areas may negatively affect adhesion of themulti-stacked electronic device to the PCB.

SUMMARY

According to an embodiment of the present disclosure, a method includes:forming a multi-stacked electronic device having two or more electroniccomponents, each of the electronic components includes a leadframe, theleadframes of each electronic component are physically joined togetherusing a non-solder metal joining process to form a joint, and the jointis located outside a solder connection region.

According to another embodiment of the present disclosure, a methodincludes: providing a first electronic component, the first electroniccomponent including a first leadframe, providing a second electroniccomponent, the second electronic component including a second leadframe,placing the first electronic component above and in close proximity withthe second electronic component to form a multi-stacked electronicdevice in a way such that the first and second leadframes partiallyoverlap in a contact region, joining the first leadframe of the firstelectronic component to the second leadframe of the second electroniccomponent using a non-solder metal joining process to form a joint inthe contact region, the joint is located outside a solder connectionregion including a bottom portion of the first leadframe, and forming asolder connection in the solder connection region, the solder connectionattaches the multi-stacked electronic device to a soldering surface.

According to another embodiment of the present disclosure, a structureincludes: a multi-stacked electronic device having two or moreelectronic components, each of the electronic components includes aleadframe, the leadframes of each electronic component are physicallyjoined together by a joint located outside a solder connection region,the solder connection region including a portion of one of theleadframes, a solder connection exists in the portion of one of theleadframes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a multi-stacked electronic device depicting asolder connection region, according to an embodiment of the presentdisclosure;

FIG. 2 is a side view of FIG. 1;

FIG. 3 is a front view of the multi-stacked electronic device depictingforming a joint outside the solder connection region, according to anembodiment of the present disclosure;

FIG. 4 is a side view of FIG. 3; and

FIG. 5 is a front view of a multi-stacked electronic device depictingforming joints outside the solder connection region, according to anembodiment of the present disclosure.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it may be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill of the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention. It will be understood that whenan element as a layer, region, or substrate is referred to as being “on”or “over” another element, it may be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” or “directly over” anotherelement, there are no intervening elements present. It will also beunderstood that when an element is referred to as being “beneath,”“below,” or “under” another element, it may be directly beneath or underthe other element, or intervening elements may be present. In contrast,when an element is referred to as being “directly beneath” or “directlyunder” another element, there are no intervening elements present.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

In current packaging technologies, multiple leadframes extending fromthe electronic components of a multi-stacked electronic device may bejoined together at an area generally located at the lowest portion ofthe leadframes. This area may correspond with a solder connection regionof the multi-stacked electronic device. The solder connection region ofthe multi-stacked electronic device may include a solderable area bywhich the multi-stacked electronic device may be attached to, forexample, a circuit board. Several problems have been observed whenleadframes are joined near the solder connection region, includingoxidation of leadframes and solder dewetting which may cause poor bondbetween the multi-stacked electronic device and the circuit board. Itmay be desirable or advantageous to move the location of the connectionbetween leadframes from the solder connection region to a location awayfrom the solder connection region of the multi-stacked electronicdevice. Moving the connection between leadframes away from the solderconnection region may improve solderability and improve solder adhesionwhen soldering the multi-stacked electronic devices to a circuit board.

The present invention generally relates to electronic devices and moreparticularly to multi-stacked electronic devices having improvedsolderability. One way to improve solderability may include changing thelocation of a joint or connection between leadframes to an area locatedoutside a solder connection region of a leadframe of the multi-stackedelectronic device. One embodiment by which to improve solderability isdescribed in detail below by referring to the accompanying drawings inFIGS. 1-5.

Referring now to FIGS. 1-2, a multi-stacked electronic device 100 isformed or provided, according to an embodiment of the presentdisclosure. FIGS. 1 and 2 are a front view and a side view of themulti-stacked electronic device 100, respectively. The multi-stackedelectronic device 100 may be composed of an electronic component 10 avertically stacked on top of another electronic component 10 b. Theelectronic components 10 a, 10 b may include any electronic componentthat which may be joined together in multiples and subsequently solderedto a circuit board. Examples of electronic components may includestacked semiconductors, capacitors, resistors, inductors or hybridcombination. In an embodiment, the electronic components 10 a, 10 b mayeach be a tantalum capacitor. It should be noted that while only twoelectronic components are depicted in the figure, the multi-stackedelectronic device 100 may include any number of electronic devicesarranging in any imaginable configuration.

The electronic component 10 a may include a leadframe 14 a, while theelectronic component 10 b may include a leadframe 14 b. The leadframes14 a, 14 b may provide a metallized surface capable of withstanding asubsequent non-solder metal joining process, including, but not limitedto, welding or brazing. The leadframes 14 a, 14 b may extend from eachof the electronic components 10 a, 10 b, respectively. In someembodiments, the leadframes 14 a, 14 b may include preplated copperleadframes, preplated iron leadframes, preplated alloy 42 leadframes orbare metal leadframes.

The multi-stacked electronic device 100 may include a solder connectionregion 12 by which the multi-stacked electronic device 100 may beattached to, for example, a circuit board or another electronic device.In the depicted embodiment, the solder connection region 12 is locatedon a bottom portion of the leadframe 14 a of the electronic component 10a. In one embodiment, the solder connection region 12 may extend from abottom portion of the leadframe 14 a up to approximately ⅓ of a heightof the leadframe 14 a. In another embodiment, the solder connectionregion 12 may extend from the bottom portion of the leadframe 14 a up toapproximately ¼ of the height of the leadframe 14 a. In a preferredembodiment, the solder connection region 12 of the multi-stackedelectronic device 100 may include any area of the leadframe 14 a asdefined by a supplier's specification. It should be noted that thesolder connection region 12 may generally be defined by an area of theleadframe which becomes fully wetted by solder during subsequentsoldering and attachment of the multi-stacked package 100 to a circuitboard. Therefore, the various heights of the solder connection region 12disclosed above may depend on how far the solder wets or wicks up theleadframe.

In the depicted embodiment, the leadframe 14 a may extend from theelectronic component 10 a down to the solder connection region 12, andthe leadframe 14 b of the electronic component 10 b may extend upwardand may at least partially overlap the leadframe 14 a of the electroniccomponent 10 a. This configuration may allow joining the leadframes 14a, 14 b in a contact region 18 located above the solder connectionregion 12 of the leadframe 14 a. It should be noted that in typicalstacking configurations, both leadframes 14 a, 14 b may extend downwardsand joined in the solder connection region 12. Moving the location ofthe contact region 18 to an area above the solder connection region 12may reduce or eliminate wettability problems described above and improvesolderability of the multi-stacked electronic device 100.

Referring now to FIGS. 3-4, a non-solder metal joining process may beconducted to form a joint 24 between the leadframes 14 a, 14 b. Themetal joining process may include, for example, brazing or welding ofthe leadframes 14 a, 14 b together in the contact region 18 (FIG. 1). Inone embodiment, the joint 24 may include a spot weld.

At this point of the manufacturing process, a soldering surface 16 maybe formed or provided. In one embodiment, the soldering surface 16 maybe, for example, a multilayered printed circuit board (PCB) consistingof an epoxy dielectric material with a metal foil (such as copper) onits upper and lower surfaces. In another embodiment, the solderingsurface 16 may include a PCB, a circuit board, a laminate substrate, orother electronic device.

After joining the leadframes 14 a, 14 b together in the contact region18 (FIG. 1), the multi-stacked electronic device 100 may be placed onthe soldering surface 16 and a soldering process may be used to attachthe multi-stacked electronic device 100 to the soldering surface 16.More specifically, a portion of the leadframe 14 a within the solderconnection region 12 may be joined to the soldering surface 16 with asolder connection. In doing so, solder may not wet above the solderconnection region 12, which means the resulting solder connection willnot be contaminated by the joint 24. The soldering process may includemelting and flowing a filler metal or solder in the solder connectionregion 12. Preferably, in all cases, the solder may exhibit a lowermelting point than either the join 24 or any of the adjoining metals. Inone exemplary embodiment, the solder may include a lead free solder.

Referring now to FIG. 5, a multi-stacked electronic device 200 is shown,according to an embodiment of the present disclosure. The multi-stackedelectronic device 200 may be composed of electronic components 10 a, 10b and 10 c which may be vertically stacked one on top of another. Inthis embodiment, the leadframe 14 a may extend from the electroniccomponent 10 a down to the solder connection region 12, the leadframe 14b of the electronic component 10 b may extend up and may at leastpartially overlap the leadframe 14 a, and the leadframe 14 c of theelectronic component 10 c may extend up and may also at least partiallyoverlap the leadframe 14 a of the electronic component 10 a.Subsequently joints 24 may be formed on the overlapping regions betweenleadframes to physically connect the leadframes 14 a, 14 b and 14 a, 14c. As may be observed, the joints 24 are positioned above the solderconnection region 12 of the multi-stacked electronic device 200 toprevent solderability issues discussed above.

Therefore, by changing the location of the joint 24, and moving it fromthe bottom of the leadframes in the solder connection region 12 to acontact region 18 (FIG. 1) located above the solder connection region12, leadframes oxidation and solder dewetting may be prevented therebyreducing the presence of areas with poor solderability in the solderconnection region 12, this may in turn improved adhesion of themulti-stacked electronic device 100 to the soldering surface 16. Bypreventing solder dewetting, unbonded areas or defective solder jointsmay be reduced improving overall component reliability, meetingsoldering quality standards, and decreasing rework and manufacturingdelays.

What is claim is:
 1. A structure comprising: a stacked electronic devicehaving at least first and second electronic components, the firstelectronic component including a lateral, outside downwardly extendingfirst leadframe, the second electronic component including a lateral,upwardly extending leadframe, the second leadframe extending upwardly,laterally inside of, and vertically overlapping with, the firstleadframe, wherein the first and second leadframes include respectiveoverlapping portions, and the first leadframe includes a lower portionspaced from said overlapping portions and defining a solder connectionregion for soldering the stacked electronic device to a solderingsurface; and a joint located outside the solder connection region, anddirectly between and physically joining together the overlappingportions of the first and second leadframes to join the first and secondelectronic components together.
 2. The structure of claim 1, wherein thefirst electronic component is an uppermost electronic component, and thesecond electronic component is a lowermost electronic component, and theleadframe of the uppermost electronic component partially overlaps theleadframe of the lowermost electronic component.
 3. The structure ofclaim 1, wherein the solder connection region comprises a predefinedsolderable.
 4. The structure of claim 1, further comprising: a solderingsurface to which the stacked electronic device is attached by the solderconnection through the portion of one of the leadframes.
 5. Thestructure of claim 4, wherein the soldering surface comprises a circuitboard, a laminate substrate, or other electronic device.
 6. Thestructure of claim 1, wherein each of the first and second electroniccomponents comprise tantalum capacitors.